The aim of this work is to determine the DNA sequence organization of class I genes contained in the swine major histocompatibility complex (SLA). We have established that this gene family in the miniature swine contains only seven members, making it amenable for a comprehensive analysis. To date, we have isolated six of these genes. DNA sequence analysis is complete for three of the genes and nearly complete for two more. It has been established that the sequence organization of the class I SLA genes is similar to that of other class I genes. Within the family, it is possible to define at least two sub- families, based on their sequences. Homologies between the SLA genes range from 85% between the two genes within a sub-family, to 60% between sub-families. Complex alterations are observed, consistent with the interpretation that some mechanism of gene conversion may operate to generate polymorphism in this family. Physical mapping of the genes has established a tight linkage of the family, consistent with genetic data.